Hollow charges are understood to be such charges that consist of an explosive charge enclosed in a container which, forwardly in the envisaged effective direction of flight, is terminated by a conically or spherically segment-shaped metal insert of limited thickness and which, with its convex side, is turned to face towards the explosive, and with its concave side turned to face towards the intended target and which thus gives rise to a hollowing out of the charge proper forwardly in the effective direction of flight (hence the German designation Hohlladung).
Depending on the shape of this metal insert, the charge, on being initiated from the opposite side to the side of the insert and mostly from the metal in the insert will either form a jet of particles which is flung at great speed towards the target or, alternatively, the available metal will be more or less held together as a cohesive body, a so-called "slug", which is flung in a direction towards the target at very great speed. The jet-forming hollow charges will have the best effect and penetration of, for example, an armored target if they are detonated at a distance from the target which has been thoroughly tested and proven in advance. When jet-forming hollow charges are employed in projectiles of one kind or another, they are therefore provided with means which trigger the charge at exactly the right distance from the target. The projectile-forming hollow charges can, on the other hand, be triggered at more undetermined distances from the target in order to penetrate the target with their projectile or slug through the combination of mass and high velocity. Such long-distance effective, projectile-forming hollow charges are therefore often employed in booby traps and that type of so-called intelligent ammunition which is homed in over a given area which it then scans with a built-in target scanner in order, when located above the target, to fire a projectile-forming hollow charge in a direction towards the target. Both in this case and in the case of remote-fired mines, the distance to the target is indefinite and rather varying. Despite the high original velocity of the slug, it is desirable to be able to impart thereto the best possible ballistic properties, since the retarding effect of air would otherwise considerably reduce penetration into the target. If no particular measures are adopted, the rear portion of the slug will assume, for instance, a more or less manifest disc shape which significantly deteriorates the ballistic properties of the slug.
The German patent specification 33 29 969 describes the problem inherent in the configuration of the slug, at the same time as certain measures are proposed for realizing a slug which possesses good ballistic properties.
According to this patent specification, it is, namely, possible to influence the design of the slug in the desired direction, i.e. to impart to the slug a ballistically favourable shape, if one of the components included in the charge (by which is meant the explosive charge, the metal insert or the container enclosing the charge) is provided with at least three inhomogeneities symmetrically disposed in relation to the centre axis of the charge. The reason for this is that the shock wave from the detonating explosive charge will then impinge upon the insert, either with different force or at a different time, at symmetrically disposed, clearly defined points. This causes a reshaping of the slug at the relevant places. The inhomogeneity may reportedly lie in the insert, in the explosive filler, in the encapsulation of the charge or in the ignition system.
If the inhomogeneities are disposed at the insert, they can, according to the above-mentioned patent specification, consist of radially disposed machinings of the insert, for example in the form of a corrugation along its outer edge, but such machinings of the insert as radially disposed, jet-shaped continuous inhomogeneities of different densities and/or wall thicknesses are also mentioned. These are described as giving rise to fold lines along which the rear portion of the slug formed on detonation of the charge is reshaped so as approximately to be imparted the form of a number of steering fins.
The patent specification also discloses that it is fully sufficient if the inhomogeneities are of the order of magnitude of 0.1 mm.
According to European patent 0 244 507, it is possible to achieve a corresponding result if the charge is provided with inhomogeneities in the form of portions or sectors with force transmission of different intensity between the outer periphery of the insert and that sleeve which surrounds the explosive charge on other sides.
In order to achieve this object, spot crimpings or alternatively spot welding or spot gluing have been proposed in the above patent. However, all of these types of joints are difficult to render sufficiently exactly defined in order to provide the carefully pre-planned folding together of the rear portion of the slug.
The present invention now relates to a novel, simpler and more exact method of realizing portions along the outer edge of the insert with contact of varying strengths between the outer edge of the insert and the sleeve enclosing the explosive substance. According to the present invention, this is achieved in that the insert forming the forward cavity of the charge is secured into the sleeve surrounding the explosive of the charge by means of an annular portion which is disposed ahead of the insert in the effective direction of the charge and secured along the inner edge of the sleeve, the annular portion being provided with a number of symmetrically disposed grooves extending in towards the sleeve wall and forming therebetween lugs extending radially towards the center of the charge and, during formation of the slug under the action of the detonating explosive charge, function as crease formation stops. Thus, these lugs may be of a size, shape and material thickness which give the rear portion of the slug or its flaretail a number of steering fins created by fold formations which give an aerodynamically more stable projectile. The dimensions and shape of the lugs and the thickness of the annular portion must be tested for each individual case, at least until further notice.
Compared with the prior art technology, the present invention primarily offers a simpler and better defined method of realizing a per se previously known effect.
The same or similar result could thus probably be achieved with symmetrically disposed radial jet-shaped machinings in the upper surface of the insert.
The method and the apparatus according to the present invention and will now be described further in connection with the accompanying drawings.